Oral tobacco products such as snus are obtained by accommodating a tobacco material in a packaging material formed out of a material such as a nonwoven fabric. A user utilizes this oral tobacco product by placing same inside the oral cavity.
Given that the oral tobacco product is used in this manner, undesirable components contained in the tobacco material may seep out of the tobacco material into the oral cavity of the user. In this regard, Patent document 1 for instance discloses a technology for lowering the amount of nitrosamine contained in a tobacco material during the manufacturing of an oral tobacco product.
Patent document 1 discloses the feature of drying air-dried, yellowed tobacco leaves through a natural drying step and a controlled drying step, to reduce nitrite nitrogen and nitrosamine in the tobacco material.
Patent document 2 discloses an invention pertaining to a display mechanism of a drying room that is used for drying of flue-cured variety tobacco. Regarding drying of flue-cured variety tobacco, Patent document 2 discloses the feature of raising the temperature from 38° C. at an initial stage up to 68° C. ultimately, and setting a yellowing period to about 95 to 75% RH and a drying period of tobacco stems to about 50 to 20% RH.
Unlike the foregoing art, Patent document 3 discloses art relating to a smokeless tobacco composition, and mentions a coloring agent as being included in the composition.
Known drying methods of tobacco leaves include fire-drying of green wrappers that are used mainly as a material for cigars (Non-patent document 1). Non-patent document 1 discloses a standard temperature-humidity operation diagram regarding drying of tobacco leaves before leaf tobacco turns yellow (yellowing) (fermentation period: dry bulb of 35° C., wet bulb of 29 degrees C., 10 to 14 hours; color and gloss fixing period: dry bulb of 45 to 50° C., wet bulb of 32 to 34° C., 20 to 26 hours; tobacco stem drying period: dry bulb of 55 to 70° C., wet bulb of 37° C., 30 to 36 hours). Non-patent document 1 indicates that in the product obtained in accordance with the above drying method the yield of a green wrapper article was 33.5%.